The present invention relates to a device for removing a fluid substance from a conveyor belt closed on itself to form a loop and running around at least two end rollers, at least one of which is powered.
In particular, the invention relates to conveyor belts of machines and installations for painting, colouring or impregnation processes, described more simply as xe2x80x9cpaintingxe2x80x9d in the following text, which make the articles to be treated pass through a chamber for spraying the fluid treatment substance, for example the paint.
The conveyor belt has two branches: an upper, outgoing branch, on which are placed the articles to be treated and which is struck by the sprays of paint, and a lower return branch, which is splashed with paint and which has to be cleaned before it returns to the upper level, to enable the conveyor to receive new articles to be painted and to enable the removed paint to be recovered.
The devices in use at the present time for cleaning the belt comprise, in the first place, means for wetting the surface to be cleaned with solvent and subsequent means for removing the paint fluidized by the solvent, by a scraping or shaving operation, for example by means of fixed scraper blades or by means of rotating cylinders.
FIG. 1 of the attached drawing shows an example of a cleaning device with double reverse cylinders, of the type described in European patent EP 425969 held by the applicant. In this figure, the letter T indicates the final part of the conveyor of the painting machine, with its upper branch T1 and lower branch T2 running around the roller R. The cleaning device comprises a first preliminary cleaning cylinder 1, opposite and parallel to the roller R, which operates in contact with the branch T2 of T, and is made to rotate by suitable means in such a way that its periphery moves in the opposite direction to that of the branch T2, to carry out an effective action of scraping this branch and to remove from it the recovered paint which is then readily removed from the cylinder 1, by the scraping edge 102 of a trough 2 in which the recovered paint is collected and then removed and recycled by suitable means. The cylinder 1 is partially immersed in a vessel 3 containing solvent, so that the cylinder cleans itself and carries a film of the solvent into the area of contact with the lower branch T2 of T, to wet the area from which the paint is removed, and to cause the said branch T2 to leave the cylinder 1 with a small amount of solvent which has the function of softening any residual traces of paint.
Downstream from the preliminary cleaning cylinder 1 there is a finishing cylinder 5, parallel to the cylinder 1 and rotating in the same direction, which operates in contact with the branch T2 of T to remove any residual traces of paint and the film of solvent initially transferred on to T2. The paint and solvent recovered by the cylinder 5 are removed from it by the scraping edge 106 of a trough 6, in which the recovered fluid material is collected, and is then recycled together with that collected by the trough 2.
The number 4 indicates idle counter-rollers which can if necessary be provided in the various positions in which the cleaning means exert a thrust against the branch T2 of T, in order to oppose this thrust and make the action of the cleaning means more efficient.
In a system for cleaning the belt T of the type illustrated in FIG. 1, or in other known systems which comprise a succession of belt scraping units and open-topped vessels for wetting the belt with solvent and for collecting the recovered paint, the following drawbacks are encountered:
a) high evaporation of solvent from the said open-topped vessels and from the surface of the conveyor to which the solvent is applied. In this respect it should be pointed out that the whole of the cleaning equipment is located in a lower extension of the painting chamber, subject to the action of ventilation means which draw air from this chamber and discharge into the atmosphere through means of suppressing polluting products. The large surfaces affected by the solvent and by the ventilation air flow therefore cause a considerable evaporation of the solvent, which consequently becomes even less effective in its specified function;
b) it is necessary to empty and clean or replace periodically the vessel 3 of solvent under the cylinder 1 and the solvent recovery trough 6, since the recovered paint or the residue of the paint-contaminated solvent tend to accumulate on their walls;
c) whenever a painting cycle ends, the cylinders 1 and 5 have to be cleaned manually by the operators, at the cost of considerable inconvenience for them. The quality of cleaning also depends on the ability and frequently on the scrupulousness of the operators, which are not always constant factors.
The invention is designed to overcome these and other drawbacks of the known art with the following idea for a solution.
The vessel or vessels in contact with the solvent are designed and positioned in such a way that they are as nearly enclosed as possible, and the portion of conveyor belt in contact with the solvent is also isolated by suitable means from contact with the internal environment of the painting chamber, in order to prevent the evaporation of the solvent. In a preferred solution, where rotating scraping cylinders are used, the solvent vessel is located in such a way that it is enclosed by the two successive cleaning cylinders, by the portion of conveyor belt running between these cylinders, and by its side walls which are as close as possible to the said cylinders and to the said portion of conveyor belt. At the end of each painting cycle, clean solvent is made to flow into the solvent vessel and the cleaning cylinders and the conveyor belt of the painting machine are temporarily kept active so that they clean themselves.